Keywords 3D SPACE sequence - communicating hydrocephalus - hemorrhage - membranous obstruction
- obstructive hydrocephalus - susceptibility weighted imaging
Introduction
Hydrocephalus is a disorder of abnormal accumulation of cerebrospinal fluid (CSF)
within the ventricles or subarachnoid space due to the imbalance between inflow and
outflow of CSF circulation.[1 ],[2 ] It is the feature of most of the congenital and acquired brain disorders, causing
dilatation of the ventricles, which ends up in multiple complications.[2 ] Frequently, it is caused by ventricular obstruction known as noncommunicating or
obstructive hydrocephalus. Other entity is communicating or nonobstructive hydrocephalus
due to the interruption in CSF absorption or due to the overproduction of CSF.[3 ],[4 ]
Current classification of hydrocephalus divides it into noncommunicating and communicating
hydrocephalus, the latter is again divided into with cisternal obstruction or without
obstruction.[5 ],[6 ] The surgical modalities now in practice are shunt placement and endoscopic third
ventriculostomy (ETV). But, still there exists a confusion in selecting the treatment
modality, whether shunt or ETV[5 ],[7 ]
Magnetic resonance imaging (MRI) remains the primary imaging modality for the initial
evaluation of these patients, because it effectively allows detection and differentiation
of various etiologies of hydrocephalus.[8 ] Despite its sensitiveness, it falls short of exploring some hidden causes of hydrocephalus
with routinely used conventional sequences. It fails to elucidate thin membranes causing
obstruction as well as small hemorrhages associated with hydrocephalus.[9 ]
Three-dimensional sampling perfection with application optimized contrast using different
flip angle evolution (3D SPACE) sequence is an advanced MRI technique which is gaining
popularity as a sensitive imaging modality in hydrocephalus especially obstructive,
because it permits more precise identification and localization of very thin membranes
and provide useful information regarding the level of obstruction.[9 ],[10 ] 3D SPACE sequence also plays a role in communicating hydrocephalus as in tuberculous
meningitis, which is very common in developing countries such as India, by detecting
the altered signal intensity to loss of signal intensity in the basal cisterns by
inflammatory cells.[11 ] It is a modification of 3D turbo spin echo sequence where the whole imaging volume
is excited so that the images can be reconstructed in multiple planes. It uses radiofrequency
pulses with variable flip angles, which are nonselective, short refocusing pulse trains
with very high turbo factors, and high sampling efficiency. SPACE sequence can produce
high-resolution isotropic images and are less sensitive to flow, chemical shift, and
susceptibility artifacts.[9 ],[10 ]
Susceptibility Weighted Imaging (SWI) is another advanced MRI technique that demarcates
the exact site and size of the hemorrhage clearly. It is a 3D velocity compensated
gradient echo MRI sequence, which evaluates and exploits the differences in the magnetic
susceptibility of various tissues for obtaining an image.[12 ],[13 ] SWI is obtained as magnitude or phase images and combination of these two. The major
advantage we can utilize from this sequence is that it can differentiate hemorrhage
from calcification, which we cannot expect in any other sequence, even in gradient.[14 ]
To the best of our knowledge, only a few studies are there in the literature regarding
the role of 3D SPACE sequence, and there is no study regarding SWI in the assessment
of hydrocephalus. In this study, we explore the diagnostic utility of 3D SPACE sequence
and SWI in hydrocephalus and based on those findings, and we propose a simpler and
refined definition and classification of hydrocephalus, which would satisfy the selection
of treatment option.
Materials and Methods
This prospective study was conducted in our institute from January 2014 to December
2017. Approval was obtained from the ethical committee. Patients with hydrocephalus
who were referred for MRI brain were enrolled for our study. We included 109 patients
with moderate to severe hydrocephalus based on Evans index. We excluded patients >50
years (due to age related dilatation of ventricles), normal pressure hydrocephalus,
those patients with brain atrophy or ex-vacou dilatation, and those who were on treatment
or undergone shunt procedures or other surgeries. Informed consent was obtained from
all patients or caregivers.
MRI brain was done using Siemens Magnetom Aera 48 Channel 1.5 Tesla Machine (Germany)
using standardized institutional protocol, including T1W sagittal, T2W axial, FLAIR
coronal, diffusion weighted image with ADC mapping, gradient, MRA/MRV, and postcontrast
study (if needed). The additional sequences we included were as follows: 3D SPACE
sequence and SWI. 3D SPACE sequence was obtained in a sagittal plane covering all
the ventricles and cisterns.
MRI protocol for 3D SPACE and SWI was shown in [Table 1 ].
Table 1
MRI protocol for 3D SPACE sequence and SWI
Parameters
SWI
3D SPACE
MRI=Magnetic resonance imaging, 3D SPACE=Three-dimensional sampling perfection with
application optimized contrast using different flip angle evolutions, SWI=Susceptibility
weighted imaging
Repetition time (m)
58
3000
Echo time (ms)
40
526
Slice thickness (mm)
1
0.7
Field of view (mm)
230
230
Matrix
256
256
Voxel size
0.7
0.7
Number of signal averaging
2
2
Flip angle (°)
20
100
Analysis
The conventional images were reviewed independently by two senior neuroradiologists
with 10-year experience. Another two neuroradiologists with same experience analyzed
the special sequences. Comprehensive anatomy of each CSF compartment and their hydrodynamics
were studied with due care and the etiopathogenesis of hydrocephalus was arrived by
consensus. Out of 109 patients, 58 were male and 51 were female. About 42 patients
were under the age of 10 years, 39 were between 10 and 20 years, 21 were between 20
and 40 years, and 7 were between 40 and 50 years [Table 2 ].
Table 2
Age distribution in our study
Age group (years)
Number of patients
0-10
42
10-20
39
20-30
13
30-40
8
40-50
7
Total
109
The analysis was performed in a step-by-step manner. In the first step, conventional
sequences were analyzed carefully for any obstruction and were divided into communicating
and noncommunicating hydrocephalus. Our diagnostic criteria for obstructive hydrocephalus
were based on direct or indirect signs. Direct sign of obstruction was direct visualization
of membrane, mass, hemorrhage, or any other cause leading to obstruction. Indirect
signs were proximal upstream dilatation of ventricles, bulging of the CSF fluid just
proximal to the level of obstruction, and signal intensity change in proximal and
distal sites of obstruction. Accordingly with conventional sequences, we had 63 patients
of communicating and 46 patients of noncommunicating hydrocephalus.
Next step was analysis of 3D SPACE sequence in which careful scrutinization of every
image was done. All CSF pathways, especially all possible areas of obstruction were
examined with caution using 3D multiplanar reconstruction and maximum and minimum
intensity projection. The membranes causing obstruction were followed to their full
extent and again classified as obstructing and nonobstructing membranes. The obstructing
membranes were those, which divide the space into two or more compartments. Using
this sequence, 88 patients were diagnosed to have noncommunicating hydrocephalus.
Of these 88 patients, 80 patients showed intraventricular obstruction, whereas 8 patients
showed extraventricular obstruction. Remaining 21 patients showed communicating hydrocephalus.
Third step was the analysis of SWI to locate the areas of hemorrhage by examining
phase, magnitude, combined, and MIP images. In SWI, 3 patients showed intraventricular
hemorrhage (cerebral aqueduct and foramen of Magendie) causing obstructive hydrocephalus
and 24 patients showed hemorrhage at various sites (both intraventricular and extraventricular).
The percentage of communicating and noncommunicating hydrocephalus in these sequences
was compared with conventional sequences as shown in [Table 3 ] and [Table 4 ].
Table 3
Conventional sequences versus 3D SPACE
Type of hydrocephalus
Conventional sequence
3D SPACE
3D SPACE=Three-dimensional sampling perfection with application optimized contrast
using different flip angle evolutions
Communicating hydrocephalus
63 (57.7%)
21 (19.2%)
Non communicating hydrocephalus
46 (42.2%)
88 (80.7%)
With intraventricular obstruction
80 (73.7%)
With extraventricular cisternal obstruction
8 (7.3%)
Total
109 (100%)
109 (100%)
Table 4
Hemorrhages detected in conventional sequences versus SWI
Type of hydrocephalus
Conventional sequence
SWI
3D SPACE=Three-dimensional sampling perfection with application optimized contrast
using different flip angle evolutions
Communicating hydrocephalus
2 (1.8%)
9 (8.2%)
Non communicating hydrocephalus
4 (3.6%)
18 (16.5%)
Total number of hemorrhages detected
6 (5.5%)
27 (24.7%)
Diagnostic accuracy was calculated for conventional sequence, 3D SPACE sequence, and
SWI and was compared.
Results
Out of 46 noncommunicating hydrocephalus diagnosed by conventional sequences, direct
obstruction was seen in 21 patients and indirect signs of obstruction were seen in
25 patients. Direct obstruction included aqueductal membranes in two patients, tectal
glioma in one patient, pineal tumor in two patients, Arnold Chiari malformation in
four patients, and achondroplasia in one patient. Lilliquist membrane was seen in
one patient but was only partially visualized and could not be traced to its full
extent. Colloid cyst causing obstruction of foramen of Monro was seen in one patient.
One patient of Dandy Walker variant and one patient of Blake pouch cyst were also
seen. Arachnoid cyst causing obstruction of fourth ventricle was detected in two patients.
Medulloblastoma causing obstruction of fourth ventricle was seen in one patient. Metastasis
was seen in four patients out of which two patients showed hemorrhage.
Out of 63 communicating hydrocephalus diagnosed, 14 patients were diagnosed as tuberculous
meningitis, 3 patients as encephalitis, and 1 patient as leptomeningeal carcinomatosa.
Subarachnoid hemorrhage was seen in two patients and choroid plexus tumor was seen
in two patients. The cause of hydrocephalus could not be found in 41 patients with
conventional imaging and also we could not find any obstruction in these cases. In
three patients, incomplete membranes were seen in grossly dilated lateral ventricles.
In two patients, hemorrhage was seen in germinal matrix region, but we could not find
its complete extension.
In all 88 noncommunicating hydrocephalus detected by 3D SPACE sequence, the causes
of obstruction was seen directly. Overall 49 patients showed membranous obstruction
(32 at the level of aqueduct [Figure 1 ], 7 at the foramen of Magendie, 2 at the level of Lushka, 1 at the level of foramen
of Monro, and Lilliquist membrane was seen in 7 patients [Table 5 ]), 1 patient showed severe narrowing without membrane in bilateral foramen of Monro
[Figure 2 ], 1 patient showed a tiny tumor at the level of aqueduct [Figure 3 ], 3 patients showed multiple levels of obstruction seen in both aqueduct and outlet
of fourth ventricle giving the appearance of trapped ventricle [Figure 4 ], and in another patient of postmeningitis hydrocephalus, there were multiple septations
and synechia causing multicompartmental obstructive hydrocephalus [Figure 5 ]. Other patients of obstructive hydrocephalus showed the similar findings as in conventional
sequences.
Table 5
Sites of membranous obstruction on conventional and 3D SPACE sequences
Sequences
Localization of obstructive membranes
Total number of membranes
Obstructive membranes
Nonobstructive membranes
Cerebral aqueduct
Foramen of Magendie
Foramina of Luschka
Foramen of Monro
Lilliquist memb rane
Total
Lateral vent ricles
Third vent ricle
Fourth vent ricle
Cisterns
Total
SWI=Susceptibility weighted imaging
Conven tional sequences
2
0
0
0
1
3
3
0
0
0
3
6
3D SPACE
32
7
2
1
7
49
37
13
2
1
53
102
Figure 1 (A-D): (A-D) Sagittal sections of three-dimensional sampling perfection with application
optimized contrast using different flip angle evolution sequence in four different
patients showing membrane in the cerebral aqueduct causing triventricular hydrocephalus
(solid arrows). Also, there is a Lilliquist membrane in one patient (A) in the prepontine
cistern (open arrow)
Figure 2 (A and B): (A) Sagittal and (B) coronal sections of three-dimensional sampling perfection with
application optimized contrast using different flip angle evolution sequence in a
patient showing bilateral foramen of Monro narrowing (arrows) causing upstream dilatation
of both lateral ventricles. Also, multiple nonobstructing membranes are seen in lateral
ventricles (A)
Figure 3 (A-C): (A) T2 weighted axial section in a patient with hydrocephalus showing indirect signs
of obstruction at the level of aqueduct (black arrow). (B) Sagittal section of three-dimensional
sampling perfection with application optimized contrast using different flip angle
evolution sequence showing a tiny tumor (big arrow) at the level of aqueduct which
is not visualised in T2WI. (C) Magnified view of the tumor (open white arrow) at the
level of aqueduct
Figure 4 (A-D): Trapped fourth ventricle in two different patients (A and B) and (C and D). (A and
B) are three-dimensional sampling perfection with application optimized contrast using
different flip angle evolution (3D SPACE) sagittal and coronal sections of a patient
showing obstruction at the level of aqueduct and Foramen of Magendie (arrows). Upper
arrow in (A) shows aqueductal membrane. Also note the gross dilatation of lateral
and third ventricle. (C and D) are 3D SPACE sagittal and coronal sections of another
patient showing trapped fourth ventricle, (arrows) showing fourth ventricular outlet
obstruction
Figure 5 (A-D): (A and B) Multicompartmental obstructive hydrocephalus in a patient with postmeningitis
sequel, showing multiple membranes and synachia. (C and D) On follow-up after 18 months,
there was an increase in the membranes with complete obstruction of fourth ventricular
outlet
In addition to the above said findings, 37 patients of chronic hydrocephalus showed
multiple membranes in grossly dilated lateral ventricles, which did not seem to be
causing obstruction to the flow. Similar membranes were seen in dilated third ventricle
in 13 patients, in fourth ventricle in 2 patients, and in prepontine cistern in 1
patient. These membranes were seen in both communicating as well as noncommunicating
hydrocephalus, significance, and pathology of which are uncertain. Thus, in total,
we detected 102 membranes by using 3D SPACE sequence.
In cases of turbulent flow of CSF in cerebral aqueduct and outlet of fourth ventricle,
3D SPACE demonstrated flow void in 21 patients [Figure 6 ], but in conventional sequences, it was seen merely in 2 patients. All the above
findings were confirmed during surgery.
Figure 6 (A and B): (A and B) Sagittal sections of three-dimensional sampling perfection with application
optimized contrast using different flip angle evolution sequence in two different
patients showing prominent flow void at the level of aqueduct and fourth ventricle
(arrows) due to turbulent flow
SWI detected hemorrhage in 27 patients (hemorrhage at the level of aqueduct in 2 patients,
foramen of Magendie in 1 patient, chronic subarachnoid hemorrhage in 8 patients, germinal
matrix hemorrhage with intraventricular extension in 6 patients [Figure 7 ], isolated lateral ventricular hemorrhage in 3 patients, multiple hemorrhagic foci
throughout cerebral hemisphere and brainstem in 1 patient of hemorrhagic encephalitis
[Figure 8 ], hemorrhage in 2 primary tumors (1 glioma and 1 medulloblastoma), and hemorrhage
in 4 patients of metastasis. SWI detected 27 patients (24.7%) of hemorrhage in contrast
to conventional sequence, which detected only 6 patients (5.5%) as shown in [Table 6 ]. The causes of hydrocephalus in our study are enumerated in [Table 7 ].
Figure 7 (A-H): T2 weighted axial and susceptibility weighted imaging (SWI) images of four different
patients showing hemorrhage, (A and B) SWI showed hemorrhage in right germinal matrix
with intraventricular extension (arrow), which is not visible in T2WI. (C and D) another
patient showing right germinal matrix hemorrhage with intraventricular extension in
SWI (arrow) but T2WI shows a small area of hemorrhage in the germinal matrix, extension
into ventricle is not visualised. Another two patients (E and F) and (G and H) show
choroid plexus hemorrhage in SWI (arrows) which is not clear on T2WI
Figure 8 (A-D): T1 WI axial (A), T2I axial (B), susceptibility weighted imaging (SWI) images (C and
D) of a patient with hemorrhagic encephalitis; SWI shows multiple tiny hemorrhagic
foci in cerebral hemispheres and brainstem, which are not visible in T1 and T2WI images
Table 6
Sites of hemorrhage detected on conventional sequences and SWI
Sequence
Localization of hemorrhages
Total number of hemorrhage
Cerebral aqueduct
Foramen of Magendie
Sub arachnoid hemorrhage
Isolated lateral ventricular hemorrhage
Germinal matrix hemorrhage with intraventricular extension
Primary tumor/ metastasis
Encephalitis
Conventional sequence
0
0
2
0
2
2
0
6
SWI
2
1
8
3
6
6
1
27
Table 7
Causes of hydrocephalus in our study
Site
Causes
No of patients
Cerebral
Membrane
32
aqueduct
Pineal/tectal tumor
3
Aqueductal tumor
1
Hemorrhage
2
Foramen of
Stenosis
Magendie and Lushka
Membrane
7 (Magendie) + 2 (Lushka)
Congenital causes - Dandy walker + Arnold chiari + achondroplasia
2 + 4 + 1
Arachnoid cyst
2
Hemorrhage
1
Foramen of Monro
Stenosis
1
Membrane
1
Colloid cyst occlusion
1
Subarachnoid space
Lilliquist membrane
7
Hemorrhage
8
Meningitis
14
Encephalitis
3
Leptomeningeal carcinomatosa
1
Intraventricular
Extension from germinal matrix and intracranial hemorrhage
6
Isolated lateral ventricular hemorrhage
3
Choroid plexus tumors
2
Parenchymal
Metastasis
4
Medulloblastoma
1
Total
109
Among 88 patients of obstructive hydrocephalus, 54 were male and 44 were female. And
out of 21 communicating hydrocephalus, 9 were male and 12 were female [Table 8 ].
Table 8
Hydrocephalus in male versus female
Hydrocephalus
Male
Female
Total
CSF=Cerebrospinal fluid, CNS=Central nervous system, VPS=Ventriculoperitoneal shunt,
VAS=Ventriculoatrial shunt, ETV=Endoscopic third ventrculostomy, SOL=Space occupying
lesion
Non communicating
49
39
88
Communicating
9
12
21
Total
58
51
109
When compared with conventional sequence, the diagnostic accuracy of 3D SPACE sequence
in obstructive hydrocephalus is 100% (Vs 61.4%). In nine patients of communicating
hydrocephalus, etiology was detected by SWI, and in three patients of noncommunicating
hydrocephalus, level of obstruction was detected using SWI with 95% confidence interval.
Thus, SWI is more accurate in obtaining the etiology in communicating hydrocephalus
but plays a less role in noncommunicating hydrocephalus.
Discussion
Hydrocephalus is a very common clinical disorder, and effective surgical treatment
options are available according to the etiology. The success of these treatment strategies
solely depends on the accurate diagnosis and classification of this disorder.[5 ],[7 ] In literature, as aqueductal stenosis is most common cause of obstructive hydrocephalus,
most of the imaging modalities are oriented toward diagnosing this.[8 ] However, a significant number of patients with other cause of obstructive hydrocephalus
are still misdiagnosed as communicating and offered ineffective treatment option.[9 ] Over the years, advancement of MRI has helped in better understanding of CSF morphology
and flow.
Recently, 3D SPACE sequence has been proposed as rapid and most efficient sequence
for evaluating hydrocephalus.[10 ] This is because of their effectiveness in detecting thin membrane as the cause of
obstruction and better localization of obstruction. In our study, noncommunicating
hydrocephalus were detected in 80.7% of the whole cohort in contrast to 42.2% in conventional
sequence. This is mainly because of the insensitive conventional sequence in detecting
obstructive causes like thin membranes giving a spurious result of large number of
communicating hydrocephalus. We found that the obstructive membranes are not only
at the aqueductal level but also at the outlets of fourth ventricle, foramen of Monro,
and in the anterior perimesencephalic cistern as well as more membranes [49 obstructing
and 53 nonobstructing membranes (total 102) versus 3 obstructing and 3 nonobstructing
membranes (total 6)] detected than in conventional sequence. Additionally, it helped
in detecting small to very small obstructive lesions, which were missed in conventional
sequence. Recently, this special sequence was found to sensitive in detecting tuberculous
meningitis as a cause for communicating hydrocephalus, by detecting altered signal
intensity or obliteration of CSF signal intensity in basal cisterns by inflammatory
cells. Though rarely reported in western countries, this is a common entity in developing
countries such as India.
The prospective study by Dincer et al .[9 ] in 2009 showed 3D-CISS sequences to be more sensitive in diagnosing obstructive
hydrocephalus than conventional sequence by diagnosing 19.4% new cases. However, in
our study, 47.7% of new obstructive cases out of 109 patients explaining the fact
that 3D SPACE has higher resolution than 3D CISS. Similar to our study, Murat Ucar
et al . in 2014 found that 3D-SPACE yielded less artifacts and high CNR values between the
CSF and parenchyma than 3D-CISS.[15 ],[16 ] Algin et al . in 2017 stated that 3D-SPACE technique at 3T MRI better delineates the morphology
of CSF containing spaces, CSF-related tiny membranes, CSF hydrodynamics, and other
associated findings and recommended its routine use for patients with CSF disorders.[17 ] Our study proved the same.
Algin et al . in 2012 evaluated the aqueductal patency of 21 clinically suspicious patients of
aqueductal stenosis and 12 control subjects with phase contrast MRI and 3D-SPACE images.
3D space sequence detected stenosis in all patients in which PC MR showed obstructed
flow.[10 ] This study revealed an excellent correlation between 3D-SPACE and PC-MRI. In our
study, 32 patients of aqueductal obstruction were diagnosed in contrast to 13 patients
using conventional sequences. Moreover, in cases of turbulent flow of CSF in cerebral
aqueduct and outlet of fourth ventricle, 3D SPACE sequence was comparable to the sensitiveness
of phase contrast MRI, which is the gold standard for CSF flow studies.
As intracranial hemorrhage may also be a cause for obstructive hydrocephalus, we added
SWI sequence which has higher sensitivity to susceptibility effects and better visualization
of the internal architecture of hemorrhagic foci.[13 ],[18 ],[19 ] Our study supports this by detecting hemorrhage in 27 patients when compared with
6 patients detected by conventional sequence. In few of them, it was found as the
cause of obstruction, at aqueduct and rarely at foramen of Magendie. SWI sequence
in our study, also detected germinal matrix hemorrhage and chronic subarachnoid hemorrhage
as the cause for hydrocephalus in few patients, for which no previous studies were
available to compare.
In 1914, Walter Dandy and Blackfan defined hydrocephalus as merely a symptomatic designation
and classified into communicating and noncommunicating.[3 ] Russell et al . in 1949 classified it as obstructive and nonobstructive hydrocephalus.[4 ] Surgical management is the therapeutic option of choice as medical management offers
only temporary relief.[5 ] For communicating hydrocephalus, the standard surgical treatment is shunt placement[7 ] in the lateral ventricle with different drainage points – ventriculoperitoneal (most
common), ventriculopleural, and ventriculoatrial shunt and lumboperitoneal shunt,
the drainage point is lumbar intradural space. For obstructive hydrocephalus, ETV
is the treatment of choice especially with aqueductal stenosis.[7 ],[20 ] It is contraindicated in communicating hydrocephalus. Other endoscopic procedures
available are fenestration of cysts, foraminoplasty, and marsupialization. Cerebral
aqueductoplasty is an effective treatment for membranous and short-segment stenoses
of the sylvian aqueduct.[20 ] Alternatives treatments, choroid plexectomy or choroid plexus coagulation are effective
in cases of CSF over-production. In tumor causing obstruction, removal of tumor cures
the hydrocephalus in 80%.[21 ]
Thus, shunt procedures should be done only in communicating hydrocephalus and in those
whose arachnoid villi cannot absorb CSF adequately. For obstructive hydrocephalus,
where absorption of CSF is good, the endoscopic procedures are the treatment of choice.
Even though a lot of treatment options exist, already existing classification systems
pose a difficulty in arriving at a conclusion regarding the option of treatment for
the particular type of hydrocephalus. Shunt procedures are done for obstructive hydrocephalus
too nowadays increasing the morbidity and mortality due to complications.[5 ],[9 ],[22 ] So, there is an obligatory need for an exemplary terminology and thoroughgoing flawless
classification. Based on our study, we propose a simpler and refined definition and
classification, which is the modification of previous ones, pertaining to the selection
of surgical options.
We define hydrocephalus as “an active process of fluid accumulation in brain due to
imbalance between inflow and outflow of CSF caused by disturbed CSF dynamics, either
at the level of secretion, absorption or at any level of circulation.” The classification
is based on the site of disturbance of CSF dynamics. If the pathology involves the
secretion or absorption site of CSF, it is classified as communicating hydrocephalus
(inception and termination). Secreting hydrocephalus involves the true communicating
hydrocephalus, whereas absorptive hydrocephalus is an obstructive hydrocephalus at
the level of end absorption and included in the communicating hydrocephalus due to
difference in the treatment. In between these two sites, wherever the pathology resides,
it will affect the circulation only. When the circulation is disturbed, it is obviously
obstruction to its flow. So, they are grouped as obstructive or noncommunicating hydrocephalus.
The classification is summarized in [Table 9 ].
Table 9
Proposed treatment oriented classification of hydrocephalus with etiopathogenesis
and options of treatment
Type of hydrocephalus
Goals of Treatment
Level of pathology
Causes
Pathology
Treatment option
Communicating hydrocephalus (pathology at inception and termination of CSF) Secreting
and Absorptive hydrocephalus
Control of secretion and improvement of drainage
At the level of secretion (choroid plexus and minor secretory pathway)
Choroid plexus tumor
Carcinoma/papilloma
Tumor resection
Choroid plexus hyperplasia
Difuse villous hyperplasia
Endoscopic coagulation of choroid plexus
Idiopathic (rare)
Impaired regulatory mechanism of secretion of CSF
VPS or VAS along with coagulation of choroid plexus
At the level of absorption (Arachnoid or pacchioni’s granulations)
Subarachnoid hemorrhage
Plugging of arachnoid villi by clot and later by scarring and fibrosis
VPS or VAS
Meningitis (TB and others) and other CNS infection
Plugging of arachnoid villi by inflammatory cells and later by fibrosis and scarring
VPS or VAS
Normal pressure hydrocephalus
Reduced CSF resorption due to elevated superficial venous pressure which in turn elevates
pressure gradient to reabsorb CSF
VPS or VAS
Increased venous pressure in dural sinuses or jugular vein due to other causes like
thrombosis
Prevents absorption
VPS or VAS
Congenital absence of arachnoid villi (very rare)
No absorption
VPS or VAS
Noncommuniating hydrocephalus (pathology of the circulation of CSF - obstruction to
the intra or extraventricular flow) Obstructive hydrocephalus of CSF circulatory pathway
Removal of the barrier to the flow of CSF
With ventricular obstruction (ventricular obstruction by intra ventricular and extrinsic
causes) (primary or secondary)
Aqueduct:
Primary aqueductal stenosis
Aqueductal membrane
Hemorrhage
Secondary to parenchymal tumor
Arnold chiari
Triventricular hydrocephalus
Severe narrowing without membrane
Congenital/acquired due to postinfection or post hemorrhage
Causing obstruction of passage
Causing obstruction of passage
Causing obstruction of passage
ETV
ETV
ETV
Resection of tumor/ETV±biopsy ETV±decompression of posterior fossa
Fourth ventricular outlet -
Foramen of Magendie and Lushka
Membranous obstruction
Hemorrhage
Retrocerebellar cyst or tumor
Dandy walker malformation
Arnold Chiari
Other developmental malformations
Tetraventricular hydrocephalus
Congenital/acquired due to postinfection or post hemorrhage
Obstruction of passage
Posterior fossa cyst causing obstruction
Obstruction of passage
Crowding of posterior fossa
Premature skull fusion/brain malformations
ETV+aspiration of hematoma
ETV/Endoscopic fenestration of cyst into ventricles/cisterns or marsupialization
Endoscopic
procedure±decompression
Foramen of Monro
Stenosis
Membrane
Lesion (colloid cyst/CNC)
Asymmetrical if unilateral
Congenital
Congenital/acquired due to postinfection or post hemorrhage
Obstruction of passage
Endoscation of fenestration of septum pellucidum/monroplasty
Excision of cyst
Others:
Intracerebral/germinal matrix hemorrhage with intraventricular extension
Any SOL causing obstruction
Isolated lateral ventricular hemorrhage
ETV
Resection of SOL +/- ETV (if unresectable)
Endoscopic fenestration of septum pellucidum
With extra ventricular cisternal CSF pathway obstruction
Basal cisterns
Chronic meningitis
Chronic hemorrhage
Due to the formation of obstructing membranes/synechiae
Endoscopic fenestration of membranes
Subarachnoid space
Chronic meningitis
Chronic hemorrhage
Leptomeningeal carcinomatosa
Membranes: Lilliquist membrane
Other unnamed membranes
Due to the formation of obstructing membranes/synechiae
Causing obstruction of flow in SAS
In prepontine cistern below third ventricle-obstruction
Obstruction
ETV if in anterior perimesencephalic cistern or endoscopic removal of membrane/synechiae.
Chemotherapy
ETV with fenestration of membrane
Endoscopic fenestration of membrane.
In our classification of communicating hydrocephalus, there is no role for ETV since
the absorption of CSF itself is affected. Also, in secretory type of communicating
hydrocephalus, overproduction of CSF will be there which could not be completed by
the normal rate of absorption. Thus, there is either a need of extracranial CSF diversion
or eviction of the cause. In our study population, for communicating hydrocephalus,
shunting was done. In obstructive hydrocephalus explained by us, endoscopic procedure
will be the first modality of treatment either it can be endoscopic fenestration or
third ventriculostomy or marsupialization. In our study, all these patients were treated
with one of the above endoscopic procedures according to the cause. Also, 39 patients
(35.7%) would have been otherwise treated with ventriculoperitoneal shunt without
3D SPACE diagnosis.
Conclusion
3D SPACE sequence in hydrocephalus patients are very sensitive in differentiating
obstructive from communicating hydrocephalus, thereby selecting more patients as candidates
for endoscopic procedures and reducing the need and complications of shunt procedures.
SWI sequence detected hemorrhage at multiple sites and helps to unveil the cause of
hydrocephalus in many patients. We recommend to include these sequences in the set
of routine MRI sequences in cases of hydrocephalus and to follow the newer classification
of hydrocephalus as the tool for selection of surgical options.
